This invention relates to a technique for interconnecting components of an electrical assembly and, more particularly, to a method for solder bonding one component to another.
In a variety of applications of practical importance, solder bonding is utilized to attach individual electronic devices such as lasers or light-emitting diodes, or arrrays of such devices, to a mounting substrate. Further, solder bonding is also employed, for example, to bond integrated-circuit chips to a printed-circuit board. Illustratively, aligned patterns of conductive bonding pads are defined on the respective components to be connected. Typically, solder bumps are then formed on the pads of one of the components. Subsequently, the aligned pattern of pads on the other component is brought into contact with the bumps and the solder is melted. In that way, the components are electrically connected together and mechanically attached to each other.
On each component, the bonding pads to which solder is to be adhered are connected to an associated metallization pattern defined on the surface of the component. To prevent molten solder from flowing from a bonding pad area to its associated metallization pattern, either during initial formation of the solder bumps or subsequently during the attachment process, it is customary to interpose a so-called confinement or dam layer between each such pad and its associated metallization. The dam layer, which is made of a material that is substantially non-wettable by molten solder, serves to confine solder to the immediate areas of the respective bonding pads. This insures, for example, that all the solder bumps formed on a component will be of substantially the same height and will remain essentially so during the attachment process. Also, the dam blocks solder from flowing to portions of the metallization pattern where the presence of solder might interfere with subsequent wire-bonding operations.
Subsequent to formation of solder bumps on the aforedescribed bonding pads, it is often observed that randomly shaped and randomly positioned pieces of solder have been deposited on the surface of the dam layer as a result of the solder-bump-formation step. These pieces of solder debris are not securely attached to the surface of the dam layer and are, therefore, relatively free to move. Such movement of the solder debris can easily cause serious electrical, mechanical or optical problems to occur in the final component assembly package.
Accordingly, workers skilled in the art have directed efforts at trying to solve the noted solder debris problem. It was recognized that these efforts, if successful, would increase the manufacturing yield of high-reliability solder-bonded component assemblies and thereby decrease their cost.